This invention relates to vehicle deckings of the kind composed of a plurality of channels laid and fixed side-by-side, with their webs uppermost, on and crosswise of bearers secured to and running longitudinally of the chassis or frame members of the vehicle.
A typical decking assembly of the known kind referred to above, is schematically shown, in end elevation, in FIG. 1 of the drawings herewith. The decking channels 10 are fixed, by bolting or riveting (as indicated at 11) to the bearers 12 (of channel or "C" section); and these, in turn, are secured to the chassis members 13, usually with a pad or insert of hardwood or other suitable material sandwiched between them as indicated at 14.
The prior arrangement, as shown in FIG. 1, is unsatisfactory in several ways:
(A) The holes for the fastenings indicated at 11 cannot be readily drilled with the parts assembled, because the virtually continuous upper surface of the decking forbids drill access from above; and drilling upwardly, from between the flanges of the bearers, while not impossible, is at best most inconvenient.
(B) Since the lateral spacing of the chassis members 13 is predetermined, that of the bearers 12 is similarly predetermined, and this in turn sets a limit on the permissible cantilever overhang of the decking as indicated by span 15 in FIG. 1. In this connection experience has shown that with uniformly distributed overloading of the decking (of customary decking width) yield or failure of the decking is almost invariably manifested as downward bending of the cantilevered portions of the decking about the supports constituted by the bearers.
(C) With the conventional channel or "C" sectioned bearers (such as 12) there is a tendency for the chassis members (13) to twist when under severe loading conditions due to the vertical axis of maximum load intensity being relatively widely spaced from the vertical shear axis of the chassis member. This is illustrated in FIG. 1, where line 16 represents the vertical plane which contains the shear centre of the chassis member and the span 17 indicates the spacing of that centre relative to the line of maximum loading. In other words, the chassis member, viewed as a column, is under substantial eccentric loading.
(D) When cantilever failure of the decking occurs and is accompanied by deformation of the bearer, the nature of the failure is as shown (exaggeratedly) in FIG. 2 of the drawings herewith. Referring to that figure, experience has shown that strain is manifested as a reduction of the 90.degree. angle between the bearer web 18 and the bottom flange 19, while the 90.degree. angle between the web and the top flange 20 maintains its rectangularity. The result of this is the imposition of a line-contact concentrated loading at the point indicated at 21. This change in loading conditions (from a load distributed over the upper surface of flange 20 to a concentrated load at the point 21) causes local and permanent deformation of the decking members in the vicinity of point 21. And this local deformation arises even where the members concerned are, in all other respects, harmlessly strained within their elastic limits.
(E) The bearers (such as 12) have to be firmly secured to the chassis members (such as 13). This may be done by direct bolting together of the flanges 19 and 22 (if the chassis members are open-sided channels, as distinct from box members) or by the use of U-bolts and clamping plates as indicated at 23 and 24 in FIG. 1. If direct bolting is employed the drilling access disability referred to above is again encountered; moreover, the bolt-holes (in the flanges 19 and 22) are necessarily detrimentally distant from the neutral axes of the members so joined together. If U-bolting (23, 24) is employed, the drilling access difficulty is avoided, but it involves the provision of bolt-holes in the bearer webs at their most vulnerable point (i.e. remote from the neutral axis of the bearer section) and if these bolt-holes, as fractional remedy for this weakness, are made no larger than is compatible with placement of the U-bolts, some degree of inconvenience in performing that placement is inescapable.
The object of this invention is to remedy the shortcomings, itemised above as (A) to (E), in a simple manner, by the provision of a bearer by which:
(a) Easy access is provided for drilling of holes for the fastenings by which the decking members are secured to the bearers.
(b) The effective load support span (laterally of the decking) of the bearers is greater than the similar span of the chassis members; not greatly, but substantially and valuably.
(c) The vertical axes of maximum load intensity, directed downwardly by the bearers intersects, or virtually intersects, the vertical shear centres of the chassis members.
(d) In the event of strain on the part of the bearers, due to cantilever strain of the overhung decking portions, the top flanges of the bearers remain in surface contact with the decking members.
(e) Holes in the bearer webs, for acceptance of U-bolts, pierce those webs at or near the neutral axes of the bearer sections thus causing virtually no structural impairment of the bearers, and thus permitting, if desired, the holes to be considerably over-sized so to facilitate placement of the U-bolts.